Insight re: purchase

Could be very reliable if it was well kept, you can get a feel for that if the owner is forthright about what they’ve fixed and maintained. 
14 years outside, the roof could be trashed, or 14 years stored under cover and out a couple months in the summers is a different scenario. 
As you know there’s kinda 2 separate components, in general. The house and the chassis. 
In this case the house is presumably well used. (A dozen years as a “summer cabin”). Could be super easy use if it was a couple old people who spent a month a year there or could be worn the f out if it was a family with 4 kids and mooching cousins who spent all summer every summer in it. 
The chassis should be like new save for a little maintenance but that’s of little value to you if you’re just parking it too. 
Personally I’d be targeting one miles on it and light use on the house rather than the other way around. 
But it’s impossible from your description to tell if this trailer is actually a good value. 

look up mobile rv techs in your area, when buying a older rv it is well worth the couple hours of labour you might have to pay him to go look at it with you.  he will know where to look to find the issues and not be blinded by excitement like a purchaser will be.  he can also give you an estimate of what it would cost to fix the issues or if they are even worth fixing, and if you should buy it or run away. 

Make and model would help to estimate value and such.

Condition is key with older Rv's. No one on here can offer an armchair diagnosis of an old RV and all it's systems and structure especially with no details about make model or condition. Best advice - get a qualified RV inspector and have a thorough and documented inspection before you make any offer. Then you'll know what you're dealing with.